Preparation of 1, 8-diisocyanato-p-menthane



Patented Oct. 19, 1954 UNITED STATES PATENT OFFICE as.. I n 1- PREPARATION OF 1,8-DIISOCYANATO-p- MENTHANE Newman M. Bortnick, Oreland, Pa., assignor to Rohm & Haas Company, Philadelphia, Pa., a corporation of Delaware No Drawing. Application January 23, 1953,

Serial No. 332,996

4 Claims. 1 This invention relates to the preparation of 1,8-diisocyanato-p-menthane having the formula The group which is represented by R in the N 5 1H2 0H2 om CH:

0 above takes place.

NOO C a CHa The object of this invention is to produce the diisocyanate cheaply and efficiently; and this is realized by the process of this invention which comprises pyrolyzing a carbamate, which is del CH: $Ha C-NHCOOR CN=C=O 0 1 CH: heat on, CH1

23 011 CH2 CH2 basic CH: H2

\ catalyst C-NHCOOR' CN=C=O CH3 CH3 0 3 CH3 in which R. is a hydrocarbon group, preferably a lower alkyl group such as a methyl, ethyl, or isopropyl group.

The dicarbamates, from which the diisocyanate of this invention is made, are themselves prepared from 1,8-diamino-p-menthane. The latter compound is well known and is converted to the carbamates by the conventional reaction with an ester of chloroformic acid.

It has been proposed heretofore, for example, in United States Patent 2,409,712, to convert carbamates which have a primary alkyl group such as a n-butyl or a n-dodecyl group attached above general formula can be virtually any kind of a hydrocarbon group which is free of nonbenzenoid unsaturation, such as an aliphatic group typified by methyl or ethyl groups, an alicyclic group exemplified by the cyclohexyl radical, or an aromatic group such as the benzyl radical. Since, however, this group ultimately forms the alcohol ROH, it is much preferred that it be a simple lower alkyl group such as a methyl, ethyl, propyl or butyl group so that the alcohol ROH which is formed together with the diisocyanate can be easily separated from the latter by distillation.

The compound which is employed to accelerate the pyrolysis must contain a metal and must be basic. It can be a water-soluble or a Waterinsoluble, basic metallic compound. If it is of the water-soluble type, it must be at least as basic as sodium acetate. This is to say, it must be so basic that its 0.1 N aqueous solution has a pH of at least 8, and preferably from 10 to 13, at 25 C. Included in this category are the oxides, hydroxides and alkoxides of the alkali metals, sodium hydroxide, sodium methoxide, lithium oxide, potassium ethoxide, and the like, as well as the salts of the alkali metals and weak acids, especially the salts of aliphatic carboxylic acids, exemplified by sodium acetate, potassium carbonate and lithium bicarbonate. Alkali metals, e. g., sodium and potassium, can also be used, especially since they react with the alcohols formed in the process to yield alkoxides, already noted as being among the best catalysts for use in this process. Oxides and hydroxides of the alkaline earth metals are likewise operable as typified by lime, zinc oxide, magnesium oxide, barium hydroxide, strontium hydroxide, et cetera. Other basic metallic compounds which have been used successfully include the oxides and. hydroxides of cadmium, lead, mercury, manganese, iron, nickel, cobalt, cerium, copper and tin. What is required is that the catalyst be basic in the accepted sense that it forms hydroxyl ions in water or is capable of neutralizing a strong mineral acid such as hydrochloric acid or sulfuric acid.

It is recommended that from about 2% to 15% of the basic compound, based on the weight of the carbamate, be used at the outset. These amounts, however, are not critical as is evident from the fact that the ratio of basic compound to carbamate increases of necessity as the isocyanate is removed from the reactor during the progress. of the reaction.

In the preferred embodiment of this invention, the carbamate and the basic catalyst are heated together to boiling and the products, the. 1,8- diisocyanato-p-menthane and an alcohol, are distilled from the reaction mixture. It is also recommended that the pyrolysis be carried out under reduced pressure.

The following example, in which all parts are by weight, serves to illustrate the nature of this process.

Example A mixture of 1000 parts of the compound -NH 0 0 C2115 C 2 CH2 o (J-NBC o 0 02115 CH3 \CH3 and 50 parts of lime was charged to a flask equipped with a thermometer, stirrer and adapter set up for distillation under reduced pressure. Ethanol was first collected in the receiver when the pot temperature reached 140 C./4 mm. After about 55 minutes the product began to distil at 185 C./43 mm. When the temperature reached 188 C., the receiver was changed and during the following 135 minutes practically all of the material was distilled at 190 C./36 mm Petroleum ether was added to the 728 parts oi distillate and the resultant solution was extracted four times with its own volume of water. The petroleum ether solution was evaporated to remove the solvent and a residue of 583 parts was obtained. The latter was carefully fractionated and the fraction boiling at 93-6 C./0.5 mm. was isolated and identified by analysis as 1,8-diisocyanato-p-menthane. The overall yield of this product was slightly over 70%.

Essentially the same results (yields of. 60%- 80%) were obtained when the other basic compounds described above were substituted for the lime; but none of the desired diisocyanato compound was obtained in the absence of a basic catalyst.

As is known, isocyanates including the diisocyanate which is prepared by the process of this invention are valuable chemicals which are very reactive with primary and secondary amines, carboxylic acids and alcohols. They are also useful as components of adhesives wherein they promote adhesion and as modifiers for plastics, especially those of the nylon type.

This process is not only efiicient for the preparation of 1,8-diisocyanato-p-menthane but is used to advantage in the preparation of mono-isocyanates containing a tertiary-alkyl group, as disclosed in another of my applications for Letters Patent, Serial No. 311,537, filed September 25, 1952.

4 I claim: 1. A process for the preparation of 1,8-diisocyanato-p-menthane of the formula 5 -NCO o 2 OH:

H2 H2 ME c Noo C GHs which comprises pyrolyzing a carbamate of the formula 15, CH3

I C-NHCOOR C 2 CH2 H2 CH:

(8-NHCOOR CH3 OH:

Noo

C 2 CH2 (IE2 (IE2 (II-NCO 0&3 CHs which comprises pyrolyzing a carbamate' ofthe formula O-NHCOOR C a (13H;

Hz. CH2.

in which R represents an alkyl group, in the presence of a basic catalyst which isa member of the class consisting of (a) water-soluble metallic compounds of such basic strength that their 0.1 N aqueous solutions have a pH of at' least 8 at 25 C. and (b) water-insoluble metallic oxides and hydroxides, and isolating said 1,8-diisocyanato-p-menthane by distillationfrom themixe ture of said carbamate and said'basic compound. 3. A process for the preparation of 1,8'-diiso cyanato-p-menthane of the formula NHC O O C2H6 o l o CNHOOOCRH5 C 3 GHa in the presence of a basic catalyst which is a member of the class consisting of (a) Water-soluble metallic compounds of such basic strength that their 0.1 N aqueous solutions have a pH of at least 8 at 25 C. and (b) Water-insoluble metallic oxides and hydroxides, and isolating said 1,8- diisocyanato-p-menthane by distillation from the mixture of said carbamate and said basic compound.

4. A process for the preparation of 1,8-diisocyanato-p-menthane of the formula NCO C 2 CH2 Ha (E 2 CH JJ-NCO which comprises pyrolyzing a carbamate of the formula References Cited in the file of this patent UNITED STATES PATENTS Name Date Schweitzer Oct. 22, 1946 Number 

1. A PROCESS FOR THE PREPARATION OF 1,8-DIISOCYANATO-P-MENTHANE OF THE FORMULA 